1. Field of the Invention
The invention relates to a brake control system and a brake control method that control the braking force applied to the wheels of a vehicle.
2. Description of the Related Art
An electronically controlled brake apparatus that detects the control pressure at each wheel cylinder respectively provided for the wheels of a vehicle and executes a feedback control of the wheel cylinder pressure at each wheel cylinder to a target value is described in Japan Patent Application Publication No. JP-A-2005-35471. The described brake apparatus is structured to avoid application of electric current to the electromagnetic flow control valve that supplies the work fluid to the wheel cylinders for a long period in the event an abnormality causes the control pressure to deviate from the target pressure.
In a normal state of the system, application of the braking force to the respective wheels may lag the depression of the brake pedal by the driver because of the time needed to increase the control pressure to be applied to the wheel cylinders. This is because the braking control system is designed by placing the emphasis on stability, and the wheel cylinders and the pipe connected thereto exhibit elasticity as the influencing factor. When the work fluid is supplied to the wheel cylinders in response to the braking request, it is likely that the diameter of the wheel cylinder or the pipe elastically expands initially, resulting in a gentle increase in the control pressure within the wheel cylinder at the initial stage. Shortly thereafter, the control pressure will start increasing steeply to the target pressure value.
Normally, the target pressure value of the control pressure immediately after the braking request increases linearly as time passes. Accordingly the control pressure immediately after the braking request is likely to become lower than the target pressure value even in the normal state of the system. In the case where the system abnormality occurs and the braking force in accordance with the braking request cannot be normally generated, it is necessary to start another system provided for the fail safe function so as to generate the braking force.